The goal of this application is to validate nucleolin as a novel target for therapeutic intervention in cancer. The identification of nucleolin as a molecular target has resulted from the discovery of non-antisense G-rich oligonucleotides (GROs) that have profound growth inhibitory effects against many solid tumor and leukemia cell lines. There is an extensive correlation between the antiproliferative activity of the GROs and their ability to bind to nucleolin protein. Nucleolin is a multifunctional nucleolar protein critically involved in cell growth, and also present on the cell surface. Levels of nucleolin are known to be elevated in malignant cells compared to normal cells, and preliminary data indicate that strategies to target nucleolin will be tumor-selective. Although the GROs themselves have considerable therapeutic potential, delivery of oligonucleotides remains a major obstacle to their clinical use, and the development of alternative nucleolin inhibitors is desirable. The investigators have already developed screening assays that can be used to identify small molecule or peptide inhibitors of nucleolin from compound libraries. Nucleolin is also accessible to rational drug design methods, due to the availability of structural information on similar proteins. Before such extensive development studies can begin, it will be necessary to further validate nucleolin as a novel target for drug discovery. The overall aim of this proposal is therefore to demonstrate that modulation of nucleolin expression or function causes tumor- selective inhibition of cell growth. To this end, cell lines that have inducible down-regulation or overexpression of nucleolin will be developed and characterized. Antisense oligonucleotides will also be used to target inhibition of nucleolin expression. To evaluate tumor-selectivity, the relationship between cell proliferation rate, levels of nucleolin, and sensitivity to GROs, will be further explored. In addition, the mechanism by which nucleolin mediates growth inhibition will be examined by determining GRO-induced changes in nucleolin, using molecular techniques and proteomics. It is anticipated that proteomics experiments to detect changes in protein expression in GRO-treated cells will also elucidate the novel mechanism of GRO effects and will potentially identify other protein targets that participate in cell growth arrest.